1. Field of the Invention
The present invention relates to a magnetic tape medium in which data is recorded and reproduced in the longitudinal direction and more particularly to a magnetic tape medium that ensures a high dimensional stability in the direction of width and is excellent in its off-track characteristics.
2. Description of the Related Art
In recent years, a quantity of information has been extraordinarily increased in accordance with the propagation of an internet or a digital recording. The capacity of a recording medium for backing up the information as data has been increasingly expanded and the density thereof has been progressively enhanced.
In the tape medium accommodated in a cartridge in a wound state as the recording medium for backing up, a linear recording type system has been put to practical use. In the linear recording type system, a fixed head having many magnetoresistive heads disposed is used for the purpose of a high capacity to record and reproduce data in the longitudinal direction of the tape. To achieve a higher capacity, various methods are employed. For instance, a short wavelength recording is carried out by reducing the thickness of a magnetic recording layer, a track density in the direction of width of the tape is increased, the thickness itself of the tape is reduced to increase the length for one reel, etc.
Further, an attempt has been made to raise the transfer speed of the data by providing many heads and increasing the relative speed between the tape and the heads. When the thickness of the magnetic recording layer is reduced to carry out the short wavelength recording, an output is undesirably decreased due to a small spacing between the magnetic recording layer and the heads, or a durability in traveling is undesirably deteriorated during traveling many times. Accordingly, various examinations have been carried out.
When the track density in the direction of width of the tape is increased, what is called an off-track inconveniently occurs that a track does not exist in or deviate from the position of the tape to be originally read by a magnetic head, due to the dimensional change of the tape itself owing to a variation in the direction of width of the tape during traveling of the tape at high speed or an environmental factor. This problem especially obviously appears in a thin film medium in which traveling characteristics become unstable and the change of the tape itself due to the environmental factor is increased. To avoid the off-track, a method in which a servo signal is recorded on the tape to take a correct tracking is proposed.
In this servo system, there is a method in which the servo signal is magnetically or optically recorded on the magnetic layer side or the back layer side of the tape. As for the variation in the direction of width during traveling of the tape which is one of the factors of the occurrence of the off-track in the direction of width of the tape, a method has been proposed for improving a flapping phenomenon in the edge of the tape, as disclosed in Japanese Patent Application Laid-Open No. 2003-132526. As another method for decreasing the dimensional change of the tape itself due to the environmental factor, a method has been proposed for decreasing a coefficient of thermal/hygroscopic expansion of the tape or a non-magnetic substrate, as disclosed in Japanese Patent Application Laid-Open No. hei 11-250449.
However, when the track density in the direction of width of the tape is relatively low and an allowable off-track amount (((recording track width)−(reproducing track width))/2, refer an allowable off-track amount to as an off-track margin, hereinafter) is adequately large, the dimensional change of the tape due to the environmental factor does not cause a serious problem in an actual environment. When the variation in direction of width during traveling of the tape is relatively large, this does not likewise cause a great problem.